Method and apparatus for forming composite sheets of reinforced,nonwoven fibrous materials

ABSTRACT

A process is disclosed for producing non-woven flat objects which are reinforced by means of a reinforcing inlay, in which the reinforcing inlay is electrostatically charged, then coated with a thermoplastic binder in powder form, the excess powder removed, and the inlay joined with at least one layer of a fiber fleece. The electrostatic charge is preferably produced by frictional contact of the inlay with an electrically nonconductive material, the coating is preferably accomplished by conducting the charged inlay through a fluid bed of said powder, the removal of excess powder is preferably accomplished by blowing air through the coated inlay, and the joining of the inlay with the fiber fleece is preferably accomplished by heat and pressure.

United States Patent 1 Nicolaus et al.

METHOD AND APPARATUS FOR FORMING COMPOSITE SHEETS OF REINFORCED, NONWOVEN FIBROUS MATERIALS Inventors: Horst F. E. Nicolaus; Helmut E. W. Pietsch, both of Nurnberg, Germany Vereinigte Papierwerke Schickedanz & Co., Numberg, Germany Filed: Aug. 10, 1971 Appl. No.: 170,483

Assignee:

Foreign Application Priority Data Aug. 14, 1970 Germany P 20 40 500.9

References Cited UNITED STATES PATENTS Melton 264/24 10/1969 Drum 264/24 X 3/1972 Belisle et a1. 156/272 X Primary Examiner-Philip Dier Att0rney-William lsler et al.

[57 ABSTRACT A process is disclosed for producing non-woven flat objects which are reinforced by means of a reinforcing inlay, in which the reinforcing inlay is electrostatically charged, then coated with a thermoplastic binder in powder form, the excess powder removed, and the inlay joined with at least one layer of a fiber fleece. The electrostatic charge is preferably produced by frictional contact of the inlay with an electrically nonconductive material, the coating is preferably accomplished by conducting the charged inlay through a fluid bed of said powder, the removal of excess powder is preferably accomplished by blowing air through the coated inlay, and the joining of the inlay with the fiber fleece is preferably accomplished by heat and pressure.

12 Claims, 1 Drawing Figure Patented Nov. 20, 1973 INVENTORS SH g T wE 3 m v T E U N SM R RL 690 OE Y METHOD AND APPARATUS FOR FORMING COMPOSITE SHEETS OF REINFORCED, NONWOVEN FIBROUS MATERIALS This invention concerns a process for the production of plastic-bound, non-woven textile-like flat objects, which are reinforced by means of a screen of threads, a spread-on foil or the like. The invention also concerns a unit for the continuous carrying out of this process.

Unwoven flat objects of textile fibers, of which the individual fibers are joined together by suitable binders, for example, thermoplastic materials, have long been known and are used in many cases. Since such flat objects can be prepared in very thin layers and with low surface weight, they have wide field of use, especially in the production of sanitary napkins and similar sanitary and hygienic products, for example, bandage inlays, hospital pads and the like. By a proper choice of the raw fiber as well as the binder it has been possible to give such fleece materials great softness and a pleasant feel, properties which are also associated with high absorption power and especially fluid permeability and considerable wet strength. To increase the tear strength, both in the dry and the wet condition, the idea is also known of working into the fleece inlays in the form of threads, thread arrangements or the like, which may, for example, be joined with the raw fleece, but which may also be imbedded in the raw fleece in such manner that both sides of the finished product have a cloth or textile nature.

From German Pat. No. 844,789 the idea is known of giving to the reinforcing inlays, which are produced there, for example, by pressing on suitable plastics, the form of a rhomboid pattern, by which the advantage is gained that the strength of the fleece is increased almost equally lengthwise and crosswise, as the case may be. To achieve this, the idea is known of using the binder in the form of solution in suitable organic solvents or in the form of suspensions. By the choice of a low concentration of these solutions or suspensions, it is possible to keep low the total amount of binder to be applied on the fleece. On the other hand, however, with the use of dilute solutions or suspensions, it must be noted that these, when applied to the raw fleece, tend to wander into the fleece, so that the pattern printed on is not as sharply formed as would be desirable. It is true that the local concentration of the binder is decreased in this way, but through the said wandering there is an increase of the wetted surface, which is not desirable.

To avoid the disadvantages associated with the use of melted, dissolved or suspended binder, it was proposed in German Pat. No. 1,065,363 that solid, powder-form thermoplastic binders be used, which are applied by an electrostatic printing process on the raw fleece. The equipment necessary for carrying out this process consists of a drum or a strip of suitable, electrically nonconductive material, of which the surface is charged in a pattern, by means of suitably arranged electrodes, to a high electric potential. After charging, powder-form thermoplastic binder is fed to the surface, which then clings to the charged places. The surface, laden with binder in this way, is then rolled onto the fleece to be reinforced. After this, the raw fleece is subjected to a heat treatment, in which the thermoplastic binder melts and produces the desired joining of the fibers.

The advantage of this application method is that powder-form binder can be used directly. This eliminates any subsequent drying of the fleece, as required with solutions or suspensions. The disadvantage is, however, that here also, relatively great amounts of binder must necessarily be applied.

At the present state of technology, the problem exists of proposing a process for the production of plasticjoined, nonwoven, textile-like flat objects, which are reinforced by means of a network of threads, an expanded (spread) foil, or the like, and in which the amount of the binder applied for the strengthening and binding the fleece with the reinforcing inlay, is further reduced as compared with previously known methods and products.

This problem is solved according to the invention by the face that the reinforcing inlay itself is electrostatically charged and then charged with powder-form thermoplastic binder. After this, the charged (filled) reinforcing inlay is freed of excess powder by suitable measures, for example, by air blowing, beating, vibrating or the like, and finally joined with one or more layers of unreinforced or pre-reinforced fiber fleece by the action of heat and, optionally, pressure. It has been found that by the after-treatment of the electrostatically charged (and charged with thermoplastic powder) reinforcing inlay, by far the greater amount of the binder can be dissolved again from the reinforcing inlay. The reduction of the mount of powder still adhering finally to the reinforcing inlay, goes so far that the powder can no longer be seen with the naked eye. Only by microscopic examination is it found that a very slight, extremely fine and evenly distributed amount of powder adheres to the fibers or to the network of reinforcing inlay. This small amount suffices, as tests surprisingly have shown, to produce the desired joining of the raw fleece fibers with each other and to the reinforcing inlay. The total binder content of the fleece so produced amounts, according to the intensity of the prescribed after treatment of the charged reinforcing inlay, to less than one percent by weight, but it may even be reduced to a value of 0.1 to 0.2 percent by weight.

As material for the production of the reinforcing inlay, any electrically nonconductive materials are suitable, in principle, such as have been used up to now for the production of such inlays. Especially suitable are natural materials with a high dielectric constant, such as, for example, dry cotton, foils expanded to fibers or networkds of polypropylene, polyamide or the like. With the use of materials with a great dielectric constant, the necessary electrostatic charge can be produced simply by drawing the reinforcing inlay from a suitable supply roll. The friction occurring in this way often suffices to form the necessary potential. This is especially the case when the material of the reinforcing inlay, on the one hand, and the thermoplastic binder, on the other hand, are sufficiently far apart in the electrostatic voltage series. On the other hand, it is possible, of course, to produce the electrostatic charging of the reinforcing inlay separately, by friction or brushing against a suitable electrically noncon ductive material.

According to another arrangement of the invention, the electrostatically charged reinforcing inlay is conducted through a fluid bed of powder-form thermoplastic binder. In this way, the lattice or network of reinforcing inlay is especially evenly charged with binder, which is a noticeable advantage when the excess must be loosened again by air blowing, beating, vibrating or the like. Instead of the fluid bed mentioned, the reinforcing inlay may be dusted with powder-form thermoplastic binder, by which, also, a very uniform charging can be obtained.

After the loosening of excess powder by air blowing, beating, vibrating or the like, the line, so pretreated, of reinforcing inlay, is conducted, together with one or more fiber fleeces, through a suitable heat-treating apparatus. The heated strip-drum presses, known per se, have proved especially suitable for this, since they permit a large-surface pressing of the individual layers of the fleece substance to be produced. The process described brings the advantage, also, as compared with the known process, that production speed can be quite considerably increased.

For carrying out the process of the invention, an apparatus is proposed also, which will be explained in detail hereinafter with reference to the attached drawing. The sole FIGURE shows schematically the side view of the one way of carrying out this apparatus.

The apparatus proposed consists mainly of four apparatus units 1-4, which are arranged in succession, considered in the moving direction of the reinforcing inlay 5. l in the drawing is the pull-off (unwinding) mechanism and the device for electrostatic charging, 2 is the charging (with binder) unit, 3 is the discharging unit and 4 the gluing unit.

The drawing represents the case in which a reinforcing inlay 5 of a partly expanded foil of polypropylene is to be processed. The foil is drawn from a supply roll 6, which, in the example shown, takes place with the aid of the spreading rolls 7 and 7'. The resulting friction here suffices, as a rule, to charge the foil to the desired electrostatic potential. If, with the use of another material, this should not be the case, it is possible to conduct the foil over a rotating brush mechanism 8, and in this way produce the necessary charge. Instead of the brush mechanism 8,0f course, some other suitable charging device may be used, for example, the spray electrodes, known per se, which are connected with a suitable band generator or other high voltage source.

The strip of reinforcing inlay S, drawn from the supply roll 6 and possibly expanded as well as electrostatically charged, is then conducted over detour rolls 9 through the charging (with binder) unit 2, which in the example shown is a fluid bed chamber 10. The chamber consists, in the known way, of a trough which is closed below by means ofa filter plate 11 and at the same time is separated by this from the air feed chamber 12.

The air feed chamber 12 is connected, for example, by means of a flange (collar) 13 with a blower 14, which sucks in air from outside and presses this into the fluid bed chamber.

In the chamber 10, powder-form thermoplastic binder is present, which forms the fluid bed 15 under the influence of the in-flowing air. The powder-form binder of the fluid bed clings easily to the reinforcing inlay 5, because of the electrostatic charge, and is carried by the latter out of the chamber 10.

The reinforcing inlay 5, so charged, passes then into the discharging unit 3, which in the example shown consists of an air blower 16 with a suction filter l7 arranged below it. The air blower 16 has at its air exit side many nozzle-like slits 18, below which, at a short distance, the reinforcing inlay 5 is carried along. To facilitate the conduction, guide rolls l9 and 19' are arranged, in the example shown, which may also be connected with vibrators (not shown), so that an additional beating effect is exerted on the reinforcing inlay 5.

The air blower 16 is connected through an air feed pipe 20 with the blower 21, which, optionally through a filter 22, sucks in the required blowing air.

The amount of binder blown out of the reinforcing inlay is collected in the suction filter 17 and can be fed for later use. The suction filter 17 has inside it a filter inset 23 and is joined in the lower part, through a suction line 24, with a suction blower 25.

After the strip of reinforcing inlay 5 is freed of excess clinging binder, it goes into the gluing unit 4, which in the example shown is a heated band-drum press. This press consists, in the known way, of the heated drum 26, which is seated to rotate in the direction of the arrow 27. The greater part of the jacket surface of the heated drum 26 is covered with a strip 28 which turns with it, which is conducted with the aid of detour rolls 29 and tension roll 30. The strip of reinforcing inlay 5 enters this press at 31; in the example shown, the two raw fleeces 32 and 33 run in with it. The two raw fleeces are supported on the supply rolls 34 and 35 and are drawn off from there by means not shown.

In the press 26, 28, the layered material is subjected to a gentle heat and pressure treatment and emerges from same as the finished reinforced fleece 36, and can then be wound up at 37.

It is to be understood that the forms of our invention, herewith shown and described, are to be taken as preferred examples of the same, and that various changes may be made in the shape, size and arrangement of parts thereof, without departing from the spirit of the invention or the scope of the subjoined claims.

Having thus described our invention, we claim:

1. Process for the production of non-woven flat objects, which are reinforced by means of a reinforcing inlay, said method comprising the steps of electrostatically charging said reinforcing inlay, applying to said charged reinforcing inlay a thermoplastic binder in powder form, whereby to cause some of said powder to cling to said inlay, removing excess powder, and then joining said inlay with at least one layer of a fiber fleece.

2. The process, as defined in claim I, wherein said reinforcing inlay is selected from the group consisting of a lattice of threads and an expanded foil.

3. The process, as defined in claim 1, wherein the electrostatic charging of the reinforcing inlay is produced by frictional contact thereof with an electrically non-conductive material.

4. The process, as defined in claim 1, wherein said powder is applied by conducting the charged inlay through a fluid bed of said powder.

5. The process, as defined in claim 1, wherein the excess powder is removed by a method selected from the group consisting of air blowing, beating, and vibrating.

6. The process, as defined in claim 1, wherein said inlay is joined with said fiber fleece by heat and pressure.

7. Apparatus for the production of non-woven flat objects which are reinforced by means of a reinforcing inlay, said apparatus comprising means for pulling said inlay from a roll of such inlay and moving it in a predetermined path, means arranged in the path of movement of said inlay for applying to said inlay a thermoplastic resin in powder form, whereby some of said powder clings to said inlay, means for removing excess powder from said inlay, and means for joining said inlay with a fiber fleece.

blower.

11. Apparatus, as defined in claim 10, including guide rolls for conducting said inlay under said air blower, and means for vibrating said guide rolls.

12. Apparatus, as defined in claim 7, wherein said means for joining said inlay with said fiber fleece comprises a heated drum and strip means for pressing said joined inlay and fiber fleece against said drum.

k I II 

1. Process for the production of non-woven flat objects, which are reinforced by means of a reinforcing inlay, said method comprising the steps of electrostatically charging said reinforcing inlay, applying to said charged reinforcing inlay a thermoplastic binder in powder form, whereby to cause some of said powder to cling to said inlay, removing excess powder, and then joining said inlay with at least one layer of a fiber fleece.
 2. The process, as defined in claim 1, wherein said reinforcing inlay is selected from the group consisting of a lattice of threads and an expanded foil.
 3. The process, as defined in claim 1, wherein the electrostatic charging of the reinforcing inlay is produced by frictional contact thereof with an electrically non-conductive material.
 4. The process, as defined in claim 1, wherein said powder is applied by conducting the charged inlay through a fluid bed of said powder.
 5. The process, as defined in claim 1, wherein the excess powder is removed by a method selected from the group consisting of air blowing, beating, and vibrating.
 6. The process, as defined in claim 1, wherein said inlay is joined with said fiber fleece by heat and pressure.
 7. Apparatus for the production of non-woven flat objects which are reinforced by means of a reinforcing inlay, said apparatus comprising means for pulling said inlay from a roll of such inlay and moving it in a predetermined path, means arranged in the path of movement of said inlay for applying to said inlay a thermoplastic resin in powder form, whereby some of said powder clings to said inlay, means for removing excess powder from said inlay, and means for joining said inlay with a fiber fleece.
 8. Apparatus, as defined in claim 7, including means interposed between said pulling means and said applying means, for frictionally engaging said inlay, whereby to electrostatically charge said inlay.
 9. Apparatus, as defined in claim 7, wherein said applying means comprises a fluid bed chamber.
 10. Apparatus, as defined in claim 7, wherein said means for removing excess powder includes an air blower and suction means disposed below said air blower.
 11. Apparatus, as defined in claim 10, including guide Rolls for conducting said inlay under said air blower, and means for vibrating said guide rolls.
 12. Apparatus, as defined in claim 7, wherein said means for joining said inlay with said fiber fleece comprises a heated drum and strip means for pressing said joined inlay and fiber fleece against said drum. 